Efficient micro fuel cell systems and methods

ABSTRACT

Described herein are fuel cell systems and methods of using fuel cell systems. The systems include a fuel cell that generates electrical energy using hydrogen and a fuel processor that produces hydrogen from a fuel source. The fuel processor includes a reformer and a burner that heats the reformer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 10/877,771, filed Jun. 25, 2004 and entitled,“EFFICIENT MICRO FUEL CELL SYSTEMS AND METHODS”, which claims priorityunder 35 U.S.C. §119(e) from a) U.S. Provisional Patent Application No.60/482,996 filed Jun. 27, 2003, b) U.S. Provisional Patent ApplicationNo. 60/483,416 filed Jun. 27, 2003, c) U.S. Provisional PatentApplication No. 60/482,981 filed Jun. 27, 2003; each of these patentapplications is incorporated by reference herein in its entirety for allpurposes.

BACKGROUND OF THE INVENTION

The present invention relates to fuel cell technology. In particular,the invention relates to systems for improving fuel cell systemefficiency.

A fuel cell electrochemically combines hydrogen and oxygen to produceelectrical energy. The ambient air readily supplies oxygen. Hydrogenprovision, however, calls for a working supply. Gaseous hydrogen has alow energy density that reduces its practicality as a portable fuel.Liquid hydrogen, which has a suitable energy density, must be stored atextremely low temperatures and high pressures, making storing andtransporting liquid hydrogen burdensome.

A reformed hydrogen supply processes a fuel source to produce hydrogen.The fuel source acts as a hydrogen carrier. Currently availablehydrocarbon fuel sources include methanol, ethanol, gasoline, propaneand natural gas. Liquid hydrocarbon fuel sources offer high energydensities and the ability to be readily stored and transported. A fuelprocessor reforms the hydrocarbon fuel source to produce hydrogen.

Fuel cell evolution so far has concentrated on large-scale applicationssuch as industrial size generators for electrical power back-up.Consumer electronics devices and other portable electrical powerapplications currently rely on lithium ion and similar batterytechnologies. Fuel cell systems that generate electrical energy forportable applications such as electronics would be desirable but are notyet commercially available. In addition, techniques that increase fuelcell system efficiency would be beneficial.

SUMMARY OF THE INVENTION

The present invention relates to fuel cell systems and methods of usingfuel cell systems. The systems include a fuel cell that generateselectrical energy using hydrogen and a fuel processor that produceshydrogen from a fuel source. The fuel processor includes a reformer anda burner that heats the reformer.

A heat efficient fuel cell system described herein heats internalportions of a fuel cell using a heating medium from a fuel processor.The heating medium may comprise gases exhausted at high temperaturesfrom the fuel processor, which are then transported to the fuel cell.The heating medium may also include a gas that reacts catalytically inthe fuel cell to produce heat. When the gases include methanol forexample, a catalyst in the fuel cell facilitates production of heatusing the methanol. Similarly, a catalyst in the fuel cell may beemployed to facilitate heat production using hydrogen output from thereformer and provided to the fuel cell. Heating a fuel cell in thismanner allows fuel cell operating temperatures to be reached soonerduring fuel cell warm-up periods, and permits elevated operatingtemperatures to be maintained when electrical energy is not beinggenerated by the fuel cell.

Systems and methods for expediting fuel cell system start up areprovided. The systems use electrical heat to expedite start up timebefore operating temperatures are reached.

Methods for shutting down a fuel cell system are also described thatreduce the amount of moisture and gases in the reformer and in one ormore fuel cell components at shut down.

One hydrogen efficient fuel cell system described herein transportshydrogen to an inlet of a burner. The hydrogen may comprise unusedhydrogen from a fuel cell and/or hydrogen produced in a reformer. Theburner comprises a catalyst that facilitates production of heat in thepresence of the hydrogen.

In one aspect, the present invention relates to a fuel cell system forproducing electrical energy. The fuel cell system comprises a fuelprocessor and a fuel cell. The fuel processor includes a reformerconfigured to receive a fuel source, configured to output hydrogen, andincluding a catalyst that facilitates the production of hydrogen. Thefuel processor also includes a burner configured to provide heat to thereformer. The fuel cell comprises a fuel cell stack configured toproduce electrical energy using hydrogen output by the fuel processor.The fuel cell also comprises a heat transfer appendage that a) includesa portion arranged external to the fuel cell stack and b) is inconductive thermal communication with an internal portion of the fuelcell stack. The fuel cell system also comprises plumbing configured totransport a heating medium from the fuel processor to the fuel cell.

In another aspect, the present invention relates to a method forgenerating electrical energy in a fuel cell that receives hydrogen froma fuel processor. The fuel processor is configured to process a fuelsource to produce the hydrogen. The method comprises providing the fuelsource to the fuel processor. The method also comprises transporting aheating medium from the fuel processor to the fuel cell when electricalenergy output by the fuel cell includes less than an electricalthreshold or when temperature of a component in the fuel cell is lessthan a temperature threshold. The method further comprises heating aportion of the fuel cell. The method additionally comprises transportinghydrogen from the fuel processor to the fuel cell. The method alsocomprises detecting temperature of the component or electrical output ofthe fuel cell. The method further comprises generating electrical energyin the fuel cell when the temperature of the component is about equal toor greater than the threshold temperature or when electrical energyoutput by the fuel cell is about equal to or greater than an electricalthreshold.

In yet another aspect, the present invention relates to a method forshutting down a fuel cell system comprising a fuel cell that receivedhydrogen from a fuel processor. The fuel processor includes a reformerand a burner that provided heat to the reformer. The method comprisesstopping electrical energy generation in the fuel cell. The method alsocomprises discontinuing a supply of a fuel source to the reformer, whichis configured to receive the fuel source and output hydrogen. The methodfurther comprises generating heat in the burner to heat to the reformerafter discontinuing the supply of the fuel source to the reformer. Themethod additionally comprises discontinuing heat generation in theburner. The method also comprises flushing the burner with air.

In still another aspect, the present invention relates to a fuel cellsystem for producing electrical energy. The fuel cell system comprises afuel processor and a burner. The fuel processor includes a reformerconfigured to receive a fuel source, configured to output hydrogen, andincluding a catalyst that facilitates the production of hydrogen. Thefuel processor also includes a burner configured to provide heat to thereformer. The fuel cell is configured to receive hydrogen produced inthe reformer and configured to produce electrical energy using thehydrogen. The fuel cell system also comprises plumbing configured totransport hydrogen to the burner.

In another aspect, the present invention relates to a fuel cell systemfor producing electrical energy. The fuel cell system comprises a fuelprocessor and a burner. The fuel processor includes a reformerconfigured to receive a fuel source, configured to output hydrogen, andincluding a catalyst that facilitates the production of hydrogen. Thefuel processor also includes a burner configured to provide heat to thereformer. The fuel cell is configured to receive hydrogen produced inthe reformer and configured to produce electrical energy using thehydrogen. The fuel cell system also comprises plumbing configured totransport oxygen from the fuel cell to the fuel processor.

In yet another aspect, the present invention relates to a method forstarting up a fuel processor including a reformer and a burner thatprovides heat to the reformer. The method comprises generating heatusing an electrical heater that is configured to heat the burner or afuel source provided to the burner. The method also comprises supplyingthe fuel source to the burner. The method further comprisescatalytically generating heat in the burner to heat the reformer. Themethod additionally comprises supplying the fuel source to the reformer.The method also comprises generating hydrogen in the reformer.

In still another aspect, the present invention relates to a system forheating a fuel source before catalytic heat generation within a burnerincluded in a fuel processor. The system comprises a reformer configuredto receive the fuel source, configured to output hydrogen, and includinga catalyst that facilitates the production of hydrogen. The system alsocomprises a burner configured to provide heat to the reformer. Thesystem comprises an electric heater configured to heat the burner or thefuel source provided to the burner.

In another aspect, the present invention relates to a fuel cell systemfor producing electrical energy. The fuel cell system comprises a fuelprocessor. The fuel processor includes a reformer configured to receivea fuel source, configured to output hydrogen, and including a catalystthat facilitates the production of hydrogen. The fuel processor alsoincludes a burner configured to provide heat to the reformer. The fuelcell comprises a fuel cell stack configured to produce electrical energyusing hydrogen output by the fuel processor. The fuel cell alsocomprises a heat transfer appendage that a) includes a portion arrangedexternal to the fuel cell stack and b) is in conductive thermalcommunication with an internal portion of the fuel cell stack. The fuelcell system also comprises plumbing configured to transport a heatingmedium or a cooling medium between the fuel processor and the fuel cell.

In still another aspect, the present invention relates to a fuel cellsystem for producing electrical energy. The fuel cell system comprises afuel processor. The fuel processor includes a reformer configured toreceive a fuel source, configured to output hydrogen, and including acatalyst that facilitates the production of hydrogen. The fuel processoralso includes a burner configured to provide heat to the reformer. Thefuel cell comprises a fuel cell stack configured to produce electricalenergy using hydrogen output by the fuel processor. The fuel cell alsocomprises a heat transfer appendage that a) includes a portion arrangedexternal to the fuel cell stack and b) is in conductive thermalcommunication with an internal portion of the fuel cell stack. The fuelcell system also comprises control logic configured to regulate heattransfer or temperature for one or more components within the fuel cellsystem.

These and other features and advantages of the present invention will bedescribed in the following description of the invention and associatedfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a fuel cell system for producing electrical energyin accordance with one embodiment of the present invention.

FIG. 1B illustrates schematic operation for the fuel cell system of FIG.1A in accordance with a specific embodiment of the present invention.

FIG. 2A illustrates a cross sectional view of a fuel cell stack for usein the fuel cell of FIG. 1A in accordance with one embodiment of thepresent invention.

FIG. 2B illustrates an outer top perspective view of a fuel cell stackand fuel cell in accordance with another embodiment of the presentinvention.

FIG. 2C illustrates a ion conductive membrane fuel cell (PEMFC)architecture for the fuel cell of FIG. 1A in accordance with oneembodiment of the present invention.

FIG. 2D illustrates a top perspective view of bi-polar plates inaccordance with one embodiment of the present invention.

FIG. 2E illustrates a widely used and conventional bi-polar plate thatcomprises a plate/cooling layer/plate architecture.

FIG. 2F illustrates a cross sectional view of a fuel cell stack for usein the fuel cell of FIG. 1A in accordance with another embodiment of thepresent invention.

FIG. 3A illustrates a cross-sectional side view of a fuel processor usedin the fuel cell system of FIG. 1A in accordance with one embodiment ofthe present invention.

FIG. 3B illustrates a cross-sectional front view of the fuel processorused in the fuel cell system of FIG. 1A taken through a mid-plane offuel processor.

FIG. 4A illustrates a heat efficient fuel cell system in accordance withone embodiment of the present invention.

FIG. 4B illustrates a heat efficient fuel cell system in accordance withanother embodiment of the present invention.

FIG. 5 illustrates a process flow for generating electrical energy in afuel cell that receives hydrogen from a fuel processor in accordancewith one embodiment of the present invention.

FIG. 6 illustrates an embodiment of the fuel cell system of FIG. 1A thatroutes hydrogen from an anode exhaust of the fuel cell back to a burnerin the fuel processor.

FIG. 7 illustrates a process flow for shutting down a fuel cell systemcomprising a fuel cell that received hydrogen from a fuel processor inaccordance with one embodiment of the present invention.

FIG. 8 illustrates a schematic operation for a fuel cell system inaccordance with another specific embodiment of the present invention.

FIG. 9 illustrates of a system for producing electrical energy for aportable electronics device in accordance with one embodiment of thepresent invention.

FIG. 10A illustrates a system for heating a fuel source before catalyticheat generation within burner 30 in accordance with one embodiment ofthe present invention.

FIG. 10B illustrates a process flow for starting up a fuel processor inaccordance with one embodiment of the present invention.

FIG. 10C illustrates a system for electrically heating a reformer inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in detail with reference to a fewpreferred embodiments as illustrated in the accompanying drawings. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

Fuel Cell System

FIG. 1A illustrates a fuel cell system 10 for producing electricalenergy in accordance with one embodiment of the present invention. Fuelcell system 10 comprises a hydrogen fuel supply 12 and a fuel cell 20.

Hydrogen supply 12 provides hydrogen to fuel cell 20. As shown, supply12 includes a ‘reformed’ hydrogen supply that processes a fuel source toproduce hydrogen. Fuel source 17 acts as a carrier for hydrogen and canbe processed to separate hydrogen. Fuel source 17 may include anyhydrogen bearing fuel stream, hydrocarbon fuel or other hydrogen fuelsource such as ammonia. Currently available hydrocarbon fuel sources 17suitable for use with the present invention include methanol, ethanol,gasoline, propane, butane and natural gas, for example. Severalhydrocarbon and ammonia products may also produce a suitable fuel source17. Liquid fuel sources 17 offer high energy densities and the abilityto be readily stored and shipped. Storage device 16 may contain a fuelmixture. When the fuel processor 15 comprises a steam reformer, storagedevice 16 may contain a fuel mixture of a hydrocarbon fuel source andwater. Hydrocarbon fuel source/water fuel mixtures are frequentlyrepresented as a percentage fuel source in water. In one embodiment,fuel source 17 comprises methanol or ethanol concentrations in water inthe range of 1%-99.9%. Other liquid fuels such as butane, propane,gasoline, military grade “JP8” etc. may also be contained in storagedevice 16 with concentrations in water from 5-100%. In a specificembodiment, fuel source 17 comprises 67% methanol by volume.

As shown, the reformed hydrogen supply comprises a fuel processor 15 anda fuel source storage device 16. Storage device 16 stores fuel source17, and may comprise a portable and/or disposable fuel cartridge. Adisposable cartridge offers a user instant recharging. In oneembodiment, the cartridge includes a collapsible bladder within a hardplastic case. A separate fuel pump typically controls fuel source 17flow from storage device 16. If system 10 is load following, then acontrol system meters fuel source 17 to deliver fuel source 17 toprocessor 15 at a flow rate determined by the required power leveloutput of fuel cell 20.

Fuel processor 15 processes the hydrocarbon fuel source 17 and outputshydrogen. A hydrocarbon fuel processor 15 heats and processes ahydrocarbon fuel source 17 in the presence of a catalyst to producehydrogen. Fuel processor 15 comprises a reformer, which is a catalyticdevice that converts a liquid or gaseous hydrocarbon fuel source 17 intohydrogen and carbon dioxide. As the term is used herein, reformingrefers to the process of producing hydrogen from a fuel source. Fuelprocessor 15 is described in further detail below.

Fuel cell 20 electrochemically converts hydrogen and oxygen to water,generating electrical energy and heat in the process. Ambient aircommonly supplies oxygen for fuel cell 20. A pure or direct oxygensource may also be used for oxygen supply. The water often forms as avapor, depending on the temperature of fuel cell 20 components. Theelectrochemical reaction also produces carbon dioxide as a byproduct formany fuel cells.

In one embodiment, fuel cell 20 is a low volume ion conductive membrane(PEM) fuel cell suitable for use with portable applications such asconsumer electronics. A ion conductive membrane fuel cell comprises amembrane electrode assembly that carries out the electrical energygenerating electrochemical reaction. The membrane electrode assemblyincludes a hydrogen catalyst, an oxygen catalyst and a ion conductivemembrane that a) selectively conducts protons and b) electricallyisolates the hydrogen catalyst from the oxygen catalyst. A hydrogen gasdistribution layer contains the hydrogen catalyst and allows thediffusion of hydrogen therethrough. An oxygen gas distribution layercontains the oxygen catalyst and allows the diffusion of oxygen andhydrogen protons therethrough. The ion conductive membrane separates thehydrogen and oxygen gas distribution layers. In chemical terms, theanode comprises the hydrogen gas distribution layer and hydrogencatalyst, while the cathode comprises the oxygen gas distribution layerand oxygen catalyst.

A PEM fuel cell often includes a fuel cell stack having a set ofbi-polar plates. A membrane electrode assembly is disposed between twobi-polar plates. Hydrogen distribution 43 occurs via a channel field onone plate while oxygen distribution 45 occurs via a channel field on asecond facing plate. Specifically, a first channel field distributeshydrogen to the hydrogen gas distribution layer, while a second channelfield distributes oxygen to the oxygen gas distribution layer. The ‘term‘bi-polar’ refers electrically to a bi-polar plate (whether comprised ofone plate or two plates) sandwiched between two membrane electrodeassembly layers. In this case, the bi-polar plate acts as both anegative terminal for one adjacent membrane electrode assembly and apositive terminal for a second adjacent membrane electrode assemblyarranged on the opposite face of the bi-polar plate.

In electrical terms, the anode includes the hydrogen gas distributionlayer, hydrogen catalyst and bi-polar plate. The anode acts as thenegative electrode for fuel cell 20 and conducts electrons that arefreed from hydrogen molecules so that they can be used externally, e.g.,to power an external circuit. In a fuel cell stack, the bi-polar platesare connected in series to add the potential gained in each layer of thestack. In electrical terms, the cathode includes the oxygen gasdistribution layer, oxygen catalyst and bi-polar plate. The cathoderepresents the positive electrode for fuel cell 20 and conducts theelectrons back from the external electrical circuit to the oxygencatalyst, where they can recombine with hydrogen ions and oxygen to formwater.

The hydrogen catalyst separates the hydrogen into protons and electrons.The ion conductive membrane blocks the electrons, and electricallyisolates the chemical anode (hydrogen gas distribution layer andhydrogen catalyst) from the chemical cathode. The ion conductivemembrane also selectively conducts positively charged ions.Electrically, the anode conducts electrons to a load (electrical energyis produced) or battery (energy is stored). Meanwhile, protons movethrough the ion conductive membrane. The protons and used electronssubsequently meet on the cathode side, and combine with oxygen to formwater. The oxygen catalyst in the oxygen gas distribution layerfacilitates this reaction. One common oxygen catalyst comprises platinumpowder very thinly coated onto a carbon paper or cloth. Many designsemploy a rough and porous catalyst to increase surface area of theplatinum exposed to the hydrogen and oxygen.

In one embodiment, fuel cell 20 comprises a set of bi-polar platesformed from a single plate. Each plate includes channel fields onopposite faces of the plate. The single bi-polar plate thus duallydistributes hydrogen and oxygen: one channel field distributes hydrogenwhile a channel field on the opposite face distributes oxygen. Multiplebi-polar plates can be stacked to produce a ‘fuel cell stack’ in which amembrane electrode assembly is disposed between each pair of adjacentbi-polar plates.

Since the electrical generation process in fuel cell 20 is exothermic,fuel cell 20 may implement a thermal management system to dissipate heatfrom the fuel cell. Fuel cell 20 may also employ a number ofhumidification plates (HP) to manage moisture levels in the fuel cell.Further description of a fuel cell suitable for use with the presentinvention is included in commonly owned co-pending patent applicationentitled “Micro Fuel Cell Architecture” naming Ian Kaye as inventor andfiled on the same day as this patent application, which is incorporatedby reference for all purposes.

While the present invention will mainly be discussed with respect to PEMfuel cells, it is understood that the present invention may be practicedwith other fuel cell architectures. The main difference between fuelcell architectures is the type of ion conductive membrane used. In oneembodiment, fuel cell 20 is phosphoric acid fuel cell that employsliquid phosphoric acid for ion exchange. Solid oxide fuel cells employ ahard, non-porous ceramic compound for ion exchange and may be suitablefor use with the present invention. Generally, any fuel cellarchitecture may benefit from one or more systems and controlsimprovements described herein. Other such fuel cell architecturesinclude direct methanol, alkaline and molten carbonate fuel cells.

Fuel cell 20 generates dc voltage that may be used in a wide variety ofapplications. For example, electrical energy generated by fuel cell 20may be used to power a motor or light. In one embodiment, the presentinvention provides ‘small’ fuel cells that are configured to output lessthan 200 watts of power (net or total). Fuel cells of this size arecommonly referred to as ‘micro fuel cells’ and are well suited for usewith portable electronics devices. In one embodiment, fuel cell 20 isconfigured to generate from about 1 milliwatt to about 200 watts. Inanother embodiment, fuel cell 20 generates from about 3 W to about 20 W.Fuel cell 20 may also be a stand-alone fuel cell, which is a single unitthat produces power as long as it has an a) oxygen and b) hydrogen or ahydrocarbon fuel supply. A stand-alone fuel cell 20 that outputs fromabout 40 W to about 100 W is well suited for use in a laptop computer.

In one embodiment, fuel processor 15 is a steam reformer that only needssteam to produce hydrogen. Several types of reformers suitable for usein fuel cell system 10 include steam reformers, auto thermal reformers(ATR) or catalytic partial oxidizers (CPOX). ATR and CPOX reformers mixair with the fuel and steam mix. ATR and CPOX systems reform fuels suchas methanol, diesel, regular unleaded gasoline and other hydrocarbons.In a specific embodiment, storage device 16 provides methanol 17 to fuelprocessor 15, which reforms the methanol at about 250° C. or less andallows fuel cell system 10 use in applications where temperature is tobe minimized.

FIG. 1B illustrates schematic operation for fuel cell system 10 inaccordance with a specific embodiment of the present invention. Asshown, fuel cell system 10 comprises fuel container 16, hydrogen fuelsource 17, fuel processor 15, fuel cell 20, multiple pumps 21 and fans35, fuel lines and gas lines, and one or more valves 23.

Fuel container 16 stores methanol as a hydrogen fuel source 17. Anoutlet 26 of fuel container 16 provides methanol 17 into hydrogen fuelsource line 25. As shown, line 25 divides into two lines: a first line27 that transports methanol 17 to a burner 30 for fuel processor 15 anda second line 29 that transports methanol 17 to reformer 32 in fuelprocessor 15. Lines 25, 27 and 29 may comprise plastic tubing, forexample. Separate pumps 21 a and 21 b are provided for lines 27 and 29,respectively, to pressurize the lines and transmit the fuel source atindependent rates if desired. A model P625 pump as provided by Instechof Plymouth Meeting, Pa. is suitable to transmit liquid methanol forsystem 10 is suitable in this embodiment. A flow sensor or valve 23situated on line 29 between storage device 16 and fuel processor 15detects and communicates the amount of methanol 17 transfer betweenstorage device 16 and reformer 32. In conjunction with the sensor orvalve 23 and suitable control, such as digital control applied by aprocessor that implements instructions from stored software, pump 21 bregulates methanol 17 provision from storage device 16 to reformer 32.

Fan 35 a delivers oxygen and air from the ambient room through line 31to dewar 150 of fuel processor 15. Fan 35 b delivers oxygen and air fromthe ambient room through line 33 to oxygen distribution 45 in fuel cell20. In this embodiment, a model AD2005DX-K70 fan as provided by Adda USAof California is suitable to transmit oxygen and air for fuel cellsystem 10. A fan 37 blows cooling air over fuel cell 20 and its heattransfer appendages 46.

Fuel processor 15 receives methanol 17 from storage device 16 andoutputs hydrogen. Fuel processor 15 comprises burner 30, reformer 32,boiler 34 and dewar 150. Burner 30 includes an inlet that receivesmethanol 17 from line 27 and a catalyst that generates heat withmethanol presence. Boiler 34 includes an inlet that receives methanol 17from line 29. The structure of boiler 34 permits heat produced in burner30 to heat methanol 17 in boiler 34 before reformer 32 receives themethanol 17. Boiler 34 includes an outlet that provides heated methanol17 to reformer 32. Reformer 32 includes an inlet that receives heatedmethanol 17 from boiler 34. A catalyst in reformer 32 reacts with themethanol 17 and produces hydrogen and carbon dioxide. This reaction isslightly endothermic and draws heat from burner 30. A hydrogen outlet ofreformer 32 outputs hydrogen to line 39. In one embodiment, fuelprocessor 15 also includes a preferential oxidizer that interceptsreformer 32 hydrogen exhaust and decreases the amount of carbon monoxidein the exhaust. The preferential oxidizer employs oxygen from an airinlet to the preferential oxidizer and a catalyst, such as ruthenium orplatinum, that is preferential to carbon monoxide over carbon dioxide.

Dewar 150 pre-heats air before the air enters burner 30. Dewar 150 alsoreduces heat loss from fuel cell 20 by heating the incoming air beforeit escapes fuel processor 15. In one sense, dewar 150 acts as aregenerator that uses waste heat in fuel processor 15 to increasethermal management and thermal efficiency of the fuel processor.Specifically, waste heat from burner 30 may be used to pre-heat incomingair provided to burner 30 to reduce heat transfer to the air in theburner so more heat transfers to reformer 32.

Line 39 transports hydrogen from fuel processor 15 to fuel cell 20.Gaseous delivery lines 31, 33 and 39 may comprise plastic tubing, forexample. A hydrogen flow sensor (not shown) may also be added on line 39to detect and communicate the amount of hydrogen being delivered to fuelcell 20. In conjunction with the hydrogen flow sensor and suitablecontrol, such as digital control applied by a processor that implementsinstructions from stored software, fuel processor 15 regulates hydrogengas provision to fuel cell 20.

Fuel cell 20 includes an hydrogen inlet port that receives hydrogen fromline 39 and delivers it to a hydrogen intake manifold for delivery toone or more bi-polar plates and their hydrogen distribution channels. Anoxygen inlet port of fuel cell 20 receives oxygen from line 33 anddelivers it to an oxygen intake manifold for delivery to one or morebi-polar plates and their oxygen distribution channels. An anode exhaustmanifold collects gases from the hydrogen distribution channels anddelivers them to an anode exhaust port, which outlets the exhaust gasesinto the ambient room. A cathode exhaust manifold collects gases fromthe oxygen distribution channels and delivers them to a cathode exhaustport.

In addition to the components shown in shown in FIG. 1B, system 10 mayalso include other elements such as electronic controls, additionalpumps and valves, added system sensors, manifolds, heat exchangers andelectrical interconnects useful for carrying out functionality of a fuelcell system 10 that are known to one of skill in the art and omittedherein for sake of brevity.

2. Fuel Cell

FIG. 2A illustrates a cross sectional view of a fuel cell stack 60 foruse in fuel cell 20 in accordance with one embodiment of the presentinvention. FIG. 2B illustrates an outer top perspective view of a fuelcell stack 60 and fuel cell 20 in accordance with another embodiment ofthe present invention.

Referring initially to FIG. 2A, fuel cell stack 60 is a bi-polar platestack that comprises a set of bi-polar plates 44 and a set of membraneelectrode assembly (MEA) layers 62. Two MEA layers 62 neighbor eachbi-polar plate 44. With the exception of topmost and bottommost membraneelectrode assembly layers 62 a and 62 b, each MEA 62 is disposed betweentwo adjacent bi-polar plates 44. For MEAs 62 a and 62 b, top and bottomend plates 64 a and 64 b include a channel field 72 on the faceneighboring an MEA 62.

The bi-polar plates 44 in stack 60 also each include two heat transferappendages 46. More specifically, each bi-polar plate 44 includes a heattransfer appendage 46 a on one side of the plate and a heat transferappendage 46 b on the opposite side. Heat transfer appendages 46 arediscussed in further detail below.

As shown, stack 60 includes twelve membrane electrode assembly layers62, eleven bi-polar plates 44 and two end plates 64. The number ofbi-polar plates 44 and MEA layers 62 in each set may vary with design offuel cell stack 60. Stacking parallel layers in fuel cell stack 60permits efficient use of space and increased power density for fuel cell20. In one embodiment, each membrane electrode assembly 62 produces 0.7V and the number of MEA layers 62 is selected to achieve a desiredvoltage. Alternatively, the number of MEA layers 62 and bi-polar plates44 may be determined by the allowable thickness in an electronicsdevice. A fuel cell stack 60 having from one MEA 62 to several hundredMEAs 62 is suitable for many applications. A stack 60 having from aboutthree MEAs 62 to about twenty MEAs 62 is also suitable for numerousapplications. Fuel cell 20 size and layout may also be tailored andconfigured to output a given power.

Referring to FIG. 2B, top and bottom end plates 64 a and 64 b providemechanical protection for stack 60. End plates 64 also hold the bi-polarplates 44 and MEA layers 62 together, and apply pressure across theplanar area of each bi-polar plate 44 and each MEA 62. Bolts 82 a and 82b connect and secure top and bottom end plates 64 a and 64 b together.

Fuel cell 20 includes two anode ports that open to the outside of fuelcell stack 60: an inlet anode port or inlet hydrogen port 84, and anoutlet anode port or outlet hydrogen port 86. Inlet hydrogen port 84 isdisposed on top end plate 64 a, couples with an inlet line to receivehydrogen gas, and opens to an inlet hydrogen manifold 102 (see FIG. 2D)that is configured to deliver inlet hydrogen gas to a channel field 72on each bi-polar plate 44 in stack 60. Outlet port 86 receives outletgases from an anode exhaust manifold 104 (see FIG. 2D) that isconfigured to collect waste products from the anode channel fields 72 ofeach bi-polar plate 44. Outlet port 86 may provide the exhaust gases tothe ambient space about the fuel cell output the gases to a line thatcouples to port 86 for transportation of the anode exhaust gases asdescribed below.

Fuel cell 20 includes two cathode ports: an inlet cathode port or inletoxygen port (not shown), and an outlet cathode port or outletwater/vapor port 90. Inlet oxygen port is disposed on bottom end plate64 b, couples with an inlet line to receive ambient air, and opens to anoxygen manifold 106 that is configured to deliver inlet oxygen andambient air to a channel field 72 on each bi-polar plate 44 in stack 60.Outlet water/vapor port 90 receives outlet gases from a cathode exhaustmanifold 108 (see FIG. 2D) that is configured to collect water(typically as a vapor) from the cathode channel fields 72 on eachbi-polar plate 44.

FIG. 2C illustrates a ion conductive membrane fuel cell (PEMFC)architecture 120 for use in fuel cell 20 in accordance with oneembodiment of the present invention. As shown, PEMFC architecture 120comprises two bi-polar plates 44 and a membrane electrode assembly layer(or MEA) 62 sandwiched between the two bi-polar plates 44. The MEA 62electrochemically converts hydrogen and oxygen to water, generatingelectrical energy and heat in the process. Membrane electrode assembly62 includes an anode gas diffusion layer 122, a cathode gas diffusionlayer 124, a hydrogen catalyst 126, ion conductive membrane 128, anodeelectrode 130, cathode electrode 132, and oxygen catalyst 134.

Pressurized hydrogen gas (H₂) enters fuel cell 20 via hydrogen port 84,proceeds through inlet hydrogen manifold 102 and through hydrogenchannels 74 of a hydrogen channel field 72 a disposed on the anode face75 of bi-polar plate 44 a. The hydrogen channels 74 open to anode gasdiffusion layer 122, which is disposed between the anode face 75 ofbi-polar plate 44 a and ion conductive membrane 128. The pressure forceshydrogen gas into the hydrogen-permeable anode gas diffusion layer 122and across the hydrogen catalyst 126, which is disposed in the anode gasdiffusion layer 122. When an H₂ molecule contacts hydrogen catalyst 126,it splits into two H+ ions (protons) and two electrons (e−). The protonsmove through the ion conductive membrane 128 to combine with oxygen incathode gas diffusion layer 124. The electrons conduct through the anodeelectrode 130, where they build potential for use in an external circuit(e.g., a power supply of a laptop computer) After external use, theelectrons flow to the cathode electrode 132 of PEMFC architecture 120.

Hydrogen catalyst 126 breaks hydrogen into protons and electrons.Suitable catalysts 126 include platinum, ruthenium, and platinum blackor platinum carbon, and/or platinum on carbon nanotubes, for example.Anode gas diffusion layer 122 comprises any material that allows thediffusion of hydrogen therethrough and is capable of holding thehydrogen catalyst 126 to allow interaction between the catalyst andhydrogen molecules. One such suitable layer comprises a woven ornon-woven carbon paper. Other suitable gas diffusion layer 122 materialsmay comprise a silicon carbide matrix and a mixture of a woven ornon-woven carbon paper and Teflon.

On the cathode side of PEMFC architecture 120, pressurized air carryingoxygen gas (O₂) enters fuel cell 20 via oxygen port 88, proceeds throughinlet oxygen manifold 106, and through oxygen channels 76 of an oxygenchannel field 72 b disposed on the cathode face 77 of bi-polar plate 44b. The oxygen channels 76 open to cathode gas diffusion layer 124, whichis disposed between the cathode face 77 of bi-polar plate 44 b and ionconductive membrane 128. The pressure forces oxygen into cathode gasdiffusion layer 124 and across the oxygen catalyst 134 disposed in thecathode gas diffusion layer 124. When an O₂ molecule contacts oxygencatalyst 134, it splits into two oxygen atoms. Two H+ ions that havetraveled through the ion selective ion conductive membrane 128 and anoxygen atom combine with two electrons returning from the externalcircuit to form a water molecule (H₂O). Cathode channels 76 exhaust thewater, which usually forms as a vapor. This reaction in a single MEAlayer 62 produces about 0.7 volts.

Cathode gas diffusion layer 124 comprises a material that permitsdiffusion of oxygen and hydrogen protons therethrough and is capable ofholding the oxygen catalyst 134 to allow interaction between thecatalyst 134 with oxygen and hydrogen. Suitable gas diffusion layers 124may comprise carbon paper or cloth, for example. Other suitable gasdiffusion layer 124 materials may comprise a silicon carbide matrix anda mixture of a woven or non-woven carbon paper and Teflon. Oxygencatalyst 134 facilitates the reaction of oxygen and hydrogen to formwater. One common catalyst 134 comprises platinum. Many designs employ arough and porous catalyst 134 to increase surface area of catalyst 134exposed to the hydrogen or oxygen. For example, the platinum may resideas a powder very thinly coated onto a carbon paper or cloth cathode gasdiffusion layer 124.

Ion conductive membrane 128 electrically isolates the anode from thecathode by blocking electrons from passing through membrane 128. Thus,membrane 128 prevents the passage of electrons between gas diffusionlayer 122 and gas diffusion layer 124. Ion conductive membrane 128 alsoselectively conducts positively charged ions, e.g., hydrogen protonsfrom gas diffusion layer 122 to gas diffusion layer 124. For fuel cell20, protons move through membrane 128 and electrons are conducted awayto an electrical load or battery. In one embodiment, ion conductivemembrane 128 comprises an electrolyte. One electrolyte suitable for usewith fuel cell 20 is Celtec 1000 from PEMEAS USA AG of Murray Hill, N.J.(www.pemeas.com). Fuel cells 20 including this electrolyte are generallymore carbon monoxide tolerant and may not require humidification. Ionconductive membrane 128 may also employ a phosphoric acid matrix thatincludes a porous separator impregnated with phosphoric acid.Alternative ion conductive membranes 128 suitable for use with fuel cell20 are widely available from companies such as United technologies,DuPont, 3M, and other manufacturers known to those of skill in the art.For example, WL Gore Associates of Elkton, Md. produces the primeaSeries 58, which is a low temperature MEA suitable for use with thepresent invention.

In one embodiment, fuel cell 20 requires no external humidifier or heatexchanger and the stack 60 only needs hydrogen and air to produceelectrical power. Alternatively, fuel cell 20 may employ humidificationof the cathode to fuel cell 20 improve performance. For some fuel cellstack 60 designs, humidifying the cathode increases the power andoperating life of fuel cell 20.

FIG. 2D illustrates a top perspective view of bi-polar plates 44 p and44 q in accordance with one embodiment of the present invention.Bi-polar plate 44 is a single plate 44 with a first channel fields 72disposed on opposite faces 75 of the plate 44.

Functionally, bi-polar plate 44 a) delivers and distributes reactantgasses to the gas diffusion layers 122 and 124 and their respectivecatalysts, b) maintains separation of the reactant gasses from oneanother between MEA layers 62 in stack 60, c) exhausts electrochemicalreaction byproducts from MEA layers 62, d) facilitates heat transfer toand/or from MEA layers 62 and fuel cell stack 60, and e) includes gasintake and gas exhaust manifolds for gas delivery to other bi-polarplates 44 in the fuel stack 60.

Structurally, bi-polar plate 44 has a relatively flat profile andincludes opposing top and bottom faces 75 a and 75 b (only top face 75 ais shown) and a number of sides 78. Faces 75 are substantially planarwith the exception of channels 76 formed as troughs into substrate 89.Sides 78 comprise portions of bi-polar plate 44 proximate to edges ofbi-polar plate 44 between the two faces 75. As shown, bi-polar plate 44is roughly quadrilateral with features for the intake manifolds, exhaustmanifolds and heat transfer appendage 46 that provide deviation from thequadrilateral shape.

The manifold on each plate 44 is configured to deliver a gas to achannel field on a face of the plate 44 or receive a gas from thechannel field 72. The manifolds for bi-polar plate 44 include aperturesor holes in substrate 89 that, when combined with manifolds of otherplates 44 in a stack 60, form an inter-plate 44 gaseous communicationmanifold (such as 102, 104, 106 and 108). Thus, when plates 44 arestacked and their manifolds substantially align, the manifolds permitgaseous delivery to and from each plate 44.

Bi-polar plate 44 includes a channel field 72 or “flow field” on eachface of plate 44. Each channel field 72 includes one or more channels 76formed into the substrate 89 of plate 44 such that the channel restsbelow the surface of plate 44. Each channel field 72 distributes one ormore reactant gasses to an active area for the fuel cell stack 60.Bi-polar plate 44 includes a first channel field 72 a on the anode face75 a of bi-polar plate 44 that distributes hydrogen to an anode (FIG.2C), while a second channel field on opposite cathode face 75 bdistributes oxygen to a cathode. Specifically, channel field 72 aincludes multiple channels 76 that permit oxygen and air flow to anodegas diffusion layer 122, while channel field 72 b includes multiplechannels 76 that permit oxygen and air flow to cathode gas diffusionlayer 124. For fuel cell stack 60, each channel field 72 is configuredto receive a reactant gas from an intake manifold 102 or 106 andconfigured to distribute the reactant gas to a gas diffusion layer 122or 124. Each channel field 72 also collects reaction byproducts forexhaust from fuel cell 20. When bi-polar plates 44 are stacked togetherin fuel cell 60, adjacent plates 44 sandwich an MEA layer 62 such thatthe anode face 75 a from one bi-polar plate 44 neighbors a cathode face75 b of an adjacent bi-polar plate 44 on an opposite side of the MEAlayer 62.

Bi-polar plate 44 may include one or more heat transfer appendages 46.Heat transfer appendage 46 permits external thermal management ofinternal portions of fuel cell stack 60. More specifically, appendage 46may be used to heat or cool internal portions of fuel cell stack 60 suchas internal portions of each attached bi-polar plate 44 and anyneighboring MEA layers 62, for example. Heat transfer appendage 46 islaterally arranged outside channel field 72. In one embodiment,appendage 46 is disposed on an external portion of bi-polar plate 44.External portions of bi-polar plate 44 include any portions of plate 44proximate to a side or edge of the substrate included in plate 44.External portions of bi-polar plate 44 typically do not include achannel field 72. For the embodiment shown, heat transfer appendage 46substantially spans a side of plate 44 that does not include intake andoutput manifolds 102-108. For the embodiment shown in FIG. 2A, plate 44includes two heat transfer appendages 46 that substantially span bothsides of plate 44 that do not include a gas manifold.

Peripherally disposing heat transfer appendage 46 allows heat transferbetween inner portions of plate 44 and the externally disposed appendage46 via the plate substrate 89. Conductive thermal communication refersto heat transfer between bodies that are in contact or that areintegrally formed. Thus, lateral conduction of heat between externalportions of plate 44 (where the heat transfer appendage 46 attaches) andcentral portions of bi-polar plate 44 occurs via conductive thermalcommunication through substrate 89. In one embodiment, heat transferappendage 46 is integral with substrate material 89 in plate 44.Integral in this sense refers to material continuity between appendage46 and plate 44. An integrally formed appendage 46 may be formed withplate 44 in a single molding, stamping, machining or MEMs process of asingle metal sheet, for example. Integrally forming appendage 46 andplate 44 permits conductive thermal communication and heat transferbetween inner portions of plate 44 and the heat transfer appendage 46via substrate 89. In another embodiment, appendage 46 comprises amaterial other than that used in substrate 89 that is attached ontoplate 44 and conductive thermal communication and heat transfer occursat the junction of attachment between the two attached materials.

Heat may travel to or form the heat transfer appendage 46. In otherwords, appendage 46 may be employed as a heat sink or source. Thus, heattransfer appendage 46 may be used as a heat sink to cool internalportions of bi-polar plate 44 or an MEA 62. Fuel cell 20 employs acooling medium to remove heat from appendage 46. Alternatively, heattransfer appendage 46 may be employed as a heat source to provide heatto internal portions of bi-polar plate 44 or an MEA 62. In this case, acatalyst may be disposed on appendage 46 to generate heat in response tothe presence of a heating medium.

For cooling, heat transfer appendage 46 permits integral conductive heattransfer from inner portions of plate 44 to the externally disposedappendage 46. During hydrogen consumption and electrical energyproduction, the electrochemical reaction generates heat in each MEA 62.Since internal portions of bi-polar plate 44 are in contact with the MEA62, a heat transfer appendage 46 on a bi-polar plate 44 thus cools anMEA 62 adjacent to the plate via a) conductive heat transfer from MEA 62to bi-polar plate 44 and b) lateral thermal communication and conductiveheat transfer from central portions of the bi-polar plate 44 in contactwith the MEA 62 to the external portions of plate 44 that includeappendage 46. In this case, heat transfer appendage 46 sinks heat fromsubstrate 89 between a first channel field 72 on one face 75 of plate 44and a second channel field 72 on the opposite face of plate 44 to heattransfer appendage 46 in a direction parallel to a face 75 of plate 44.When a fuel cell stack 60 includes multiple MEA layers 62, lateralthermal communication through each bi-polar plate 44 in this mannerprovides interlayer cooling of multiple MEA layers 62 in stack60—including those layers in central portions of stack 60.

Fuel cell 20 may employ a cooling medium that passes over heat transferappendage 46. The cooling medium receives heat from appendage 46 andremoves the heat from fuel cell 20. Heat generated internal to stack 60thus conducts through bi-polar plate 44, to appendage 46, and heats thecooling medium via convective heat transfer between the appendage 46 andcooling medium. Air is suitable for use as the cooling medium.

As shown, heat transfer appendage 46 may be configured with a thicknessthat is less than the thickness between opposite faces 75 of plate 44.The reduced thickness of appendages 46 on adjacent bi-polar plates 44 inthe fuel cell stack 60 forms a channel 190 between adjacent appendages.Multiple adjacent bi-polar plates 44 and appendages 46 in stack formnumerous channels 190. Each channel 190 permits a cooling medium orheating medium to pass therethrough and across heat transfer appendages46. In one embodiment, fuel cell stack 60 includes a mechanical housingthat encloses and protects stack 60. Walls of the housing also provideadditional ducting for the cooling or heating medium by forming ductsbetween adjacent appendages 46 and the walls.

The cooling medium may be a gas or liquid. Heat transfer advantagesgained by high conductance bi-polar plates 44 allow air to be used as acooling medium to cool heat transfer appendages 46 and stack 60. Forexample, a dc-fan may be attached to an external surface of themechanical housing. The fan moves air through a hole in the mechanicalhousing, through channels 190 to cool heat transfer appendages 46 andfuel cell stack 60, and out an exhaust hole or port in the mechanicalhousing. Fuel cell system 10 may then include active thermal controls.Increasing or decreasing coolant fan speed regulates the amount of heatremoval from stack 60 and the operating temperature for stack 60. In oneembodiment of an air-cooled stack 60, the coolant fan speed increases ordecreases as a function of the actual cathode exit temperature, relativeto a desired temperature set-point.

For heating, heat transfer appendage 46 allows integral heat transferfrom the externally disposed appendage 46 to inner portions of plate 44and any components and portions of fuel cell 20 in thermal communicationwith inner portions of plate 44. A heating medium passed over the heattransfer appendage 46 provides heat to the appendage. Heat convectedonto the appendage 46 then conducts through the substrate 89 and intointernal portions of plate 44 and stack 60, such as portions of MEA 62and its constituent components.

In one embodiment, the heating medium comprises a heated gas having atemperature greater than that of appendage 46. As will be describedbelow, exhaust gases from burner 30 or reformer 32 of fuel processor 15may each include elevated temperatures that are suitable for heating oneor more appendages 46.

In another embodiment, fuel cell comprises a catalyst 192 disposed incontact with, or in proximity to, a heat transfer appendage 46. Thecatalyst 192 generates heat when the heating medium passes over it. Theheating medium in this case may comprise any gas or fluid that reactswith catalyst 192 to generate heat. Typically, catalyst 192 and theheating medium employ an exothermic chemical reaction to generate theheat. Heat transfer appendage 46 and plate 44 then transfer heat intothe fuel cell stack 60, e.g. to heat internal MEA layers 62. Forexample, catalyst 192 may comprise platinum and the heating mediumincludes the hydrocarbon fuel source 17 supplied to fuel processor 15(FIGS. 2A and 2F). The fuel source 17 may be heated to a gaseous statebefore it enters fuel cell 20. This allows gaseous transportation of theheating medium and gaseous interaction between the fuel source 17 andcatalyst 192 to generate heat. Similar to the cooling medium describedabove, a fan disposed on one of the walls 199 then moves the gaseousheating medium within fuel cell 20.

In a specific embodiment, the hydrocarbon fuel source 17 used to reactwith catalyst 192 comes from a reformer exhaust or burner exhaust infuel processor 15. This advantageously pre-heats the fuel source 17before receipt within fuel cell 20 and also efficiently uses or burnsany fuel remaining in the reformer or burner exhaust after processing byfuel processor 15. Alternatively, fuel cell 20 includes a separatehydrocarbon fuel source 17 feed that directly supplies hydrocarbon fuelsource 17 to fuel cell 20 for heating and reaction with catalyst 192. Inthis case, catalyst 192 may comprise platinum. Other suitable catalysts192 include palladium, a platinum/palladium mix, iron, ruthenium, andcombinations thereof. Each of these will react with a hydrocarbon fuelsource 17 to generate heat. Other suitable heating medium includehydrogen or any heated gases emitted from fuel processor 15, forexample.

When hydrogen is used as the heating medium, catalyst 192 comprises amaterial that generates heat in the presence of hydrogen, such aspalladium or platinum. As will be described in further detail below, thehydrogen may include hydrogen supplied from the reformer 32 in fuelprocessor 15.

As shown in FIGS. 2A and 2F, catalyst 192 is arranged on, and in contactwith, each heat transfer appendage 46. In this case, the heating mediumpasses over each appendage 46 and reacts with catalyst 192. Thisgenerates heat, which is absorbed via conductive thermal communicationby the cooler appendage 46. Wash coating may be employed to disposecatalyst 192 on each appendage 46. A ceramic support may also be used tobond catalyst 192 on an appendage 46.

FIG. 2F illustrates two examples in which a thermal catalyst 192 isdisposed in proximity to heat transfer appendage 46. Proximity in thiscase refers to being arranged relative to heat transfer appendage 46such that heat generated by catalyst 192 transfers to appendage 46,either by conduction, convection and/or radiation. As shown in FIG. 2F,fuel cell 20 comprises a bulkhead 195 that contains catalyst 192.Bulkhead 195 attaches to a heat transfer appendage 46 and either a)forms walls with the appendage 46 that contain catalyst 192 or b)includes its own set of wall that contain catalyst 192. Catalyst pellets192 are then disposed in bulkhead 195. The bulkhead 195 allows theheating medium to pass over and interact with catalyst 192.

As shown in FIG. 2F, the fuel cell 20 includes a mechanical housing 197that encloses and protects stack 60. Walls 199 of housing 197 andappendages 46 combine to form ducting 193. The inter-appendage ducting193 permits a) catalyst 192 to be packed into the ducting 193 and b)permits the heating medium to pass through ducting 193 and over catalyst192. In this case, catalyst 192 is packed in ducting 193 with a packingdensity loose enough to permit a gas to pass therethrough withoutencountering excessive resistance. A fan is then used to provide theheating medium into ducting 193.

For catalyst-based heating, heat then a) transfers from catalyst 192 toappendage 46, b) moves laterally though bi-polar plate 44 via conductiveheat transfer from lateral portions of the plate that include heattransfer appendage 46 to central portions of bi-polar plate 44 incontact with the MEA layers 62, and c) conducts from bi-polar plate 44to MEA layer 62. When a fuel cell stack 60 includes multiple MEA layers62, lateral heating through each bi-polar plate 44 provides interlayerheating of multiple MEA layers 62 in stack 60, which expedites fuel cell20 warm up.

Bi-polar plates 44 of FIG. 2A include heat transfer appendages 46 oneach side. In this case, one set of heat transfer appendages 46 a isused for cooling while the other set of heat transfer appendages 46 b isused for heating. Although heat transfer appendages 46 of FIG. 2F areillustrated with two different types of heating via catalyst 192(namely, by packing into ducting 193 and storage in bulkheads 195), itis understood that fuel cell 20 need not include multiple methods ofheating appendages 46 and may only include one the aforementionedtechniques. In addition, while bi-polar plates 44 illustrated in FIGS.2A and 2D show plates 44 with two heat transfer appendages 46 disposedon sides of stack 60, appendage 46 arrangements can be varied to affectand improve heat dissipation and thermal management of fuel cell stack60 according to other specific designs. For example, one or more thantwo heat transfer appendages 46 may be employed on a single plate 44 toincrease heat transfer between internal and external portions of plate44. In addition, appendages 46 need not span a side of plate 44 as shownand may be tailored based on how the heating fluid is channeled throughthe housing 197.

Although the present invention provides a bi-polar plate 44 havingchannel fields 72 that distribute hydrogen and oxygen on opposing sidesof a single plate 44, many embodiments described herein are suitable foruse with conventional bi-polar plate assemblies that employ two separateplates for distribution of hydrogen and oxygen. FIG. 2E illustrates awidely used and conventional bi-polar plate 300 that comprises aplate/cooling layer/plate architecture.

Bi-polar plate 300 includes two plates 302 a and 302 b that sandwich acooling layer 304. Top plate 302 a includes a channel field 306 a on itstop face 308 that distributes oxygen. Bottom plate 302 b includes achannel field 306 b on its bottom face 308 that distributes hydrogen (oroxygen when top plate 302 a distributes hydrogen). Cooling layer 304runs a cooling medium such as de-ionized water through cooling channels310. The cooling medium actively cools each plate 302. The coolingmedium may be routed such that the temperature increase occurs in thesame direction as reducing oxygen partial pressure in the cathode.Similar to bi-polar plate 44, bi-polar plate 300 is referred to as a‘bi-polar plate’ since it acts electrically as a cathode for one MEA andas an anode for another MEA. Bi-polar plate 300 serves similar functionsfor a fuel cell as those described above for bi-polar plate 44. Top andbottom plates 302 a and 302 b may each comprise silicon with channelsetched in their faces to provide channel fields 306.

While the present invention has mainly been discussed so far withrespect to a reformed methanol fuel cell (RMFC), the present inventionmay also apply to other types of fuel cells, such as a solid oxide fuelcell (SOFC), a phosphoric acid fuel cell (PAFC), a direct methanol fuelcell (DMFC), or a direct ethanol fuel cell (DEFC). In this case, fuelcell 20 includes components specific to these architectures, as one ofskill in the art will appreciate. A DMFC or DEFC receives and processesa fuel. More specifically, a DMFC or DEFC receives liquid methanol orethanol, respectively, channels the fuel into the fuel cell stack 60 andprocesses the liquid fuel to separate hydrogen for electrical energygeneration. For a DMFC, channel fields 72 in the bi-polar plates 44distribute liquid methanol instead of hydrogen. Hydrogen catalyst 126described above would then comprise a suitable anode catalyst forseparating hydrogen from methanol. Oxygen catalyst 134 would comprise asuitable cathode catalyst for processing oxygen or another suitableoxidant used in the DMFC, such as peroxide. In general, hydrogencatalyst 126 is also commonly referred to as an anode catalyst in otherfuel cell architectures and may comprise any suitable catalyst thatremoves hydrogen for electrical energy generation in a fuel cell, suchas directly from the fuel as in a DMFC. In general, oxygen catalyst 134may include any catalyst that processes an oxidant in used in fuel cell20. The oxidant may include any liquid or gas that oxidizes the fuel andis not limited to oxygen gas as described above. An SOFC, PAFC or MCFCmay also benefit from inventions described herein, for example. In thiscase, fuel cell 20 comprises an anode catalyst 126, cathode catalyst134, anode fuel and oxidant according to a specific SOFC, PAFC or MCFCdesign.

3. Fuel Processor

FIG. 3A illustrates a cross-sectional side view of fuel processor 15 inaccordance with one embodiment of the present invention. FIG. 3Billustrates a cross-sectional front view of fuel processor 15 takenthrough a mid-plane of processor 15 that also shows features of endplate 182. Fuel processor 15 reforms methanol to produce hydrogen. Fuelprocessor 15 comprises monolithic structure 100, end plates 182 and 184,reformer 32, burner 30, boiler 34, boiler 108, dewar 150 and housing152. Although the present invention will now be described with respectto methanol consumption for hydrogen production, it is understood thatfuel processors of the present invention may consume another fuelsource, as one of skill in the art will appreciate.

As the term is used herein, ‘monolithic’ refers to a single andintegrated structure that includes at least portions multiple componentsused in fuel processor 15. As shown, monolithic structure 100 includesreformer 32, burner 30, boiler 34 and boiler 108. Monolithic structure100 may also include associated plumbing inlets and outlets for reformer32, burner 30 and boiler 34. Monolithic structure 100 comprises a commonmaterial 141 that constitutes the structure. The monolithic structure100 and common material 141 simplify manufacture of fuel processor 15.For example, using a metal for common material 141 allows monolithicstructure 100 to be formed by extrusion. In some cases, monolithicstructure 100 is consistent in cross sectional dimensions between endplates 182 and 184 and solely comprises copper formed in a singleextrusion.

Housing 152 provides mechanical protection for internal components offuel processor 15 such as burner 30 and reformer 32. Housing 152 alsoprovides separation from the environment external to processor 15 andincludes inlet and outlet ports for gaseous and liquid communication inand out of fuel processor 15. Housing 152 includes a set of housingwalls 161 that at least partially contain a dewar 150 and provideexternal mechanical protection for components in fuel processor 15.Walls 161 may comprises a suitably stiff material such as a metal or arigid polymer, for example. Dewar 150 improves thermal heat managementfor fuel processor 15 by a) allowing incoming air to be pre-heatedbefore entering burner 30, b) dissipating heat generated by burner 32into the incoming air before the heat reaches the outside of housing152.

Referring to FIG. 3B, boiler 34 heats methanol before reformer 32receives the methanol. Boiler 34 receives methanol via fuel source inlet81, which couples to methanol supply line 27 of FIG. 1B. Since methanolreforming and hydrogen production via a catalyst 102 in reformer 32often requires elevated methanol temperatures, fuel processor 15pre-heats the methanol before receipt by reformer 32 via boiler 34.Boiler 34 is disposed in proximity to burner 30 to receive heatgenerated in burner 30. The heat transfers via conduction throughmonolithic structure from burner 30 to boiler 34 and via convection fromboiler 34 walls to the methanol passing therethrough. In one embodiment,boiler 34 is configured to vaporize liquid methanol. Boiler 34 thenpasses the gaseous methanol to reformer 32 for gaseous interaction withcatalyst 102.

Reformer 32 is configured to receive methanol from boiler 34. Walls 111in monolithic structure 100 and end walls 113 on end plates 182 and 184define dimensions for a reformer chamber 103. In one embodiment, endplate 182 and/or end plate 184 includes also channels 95 that routeheated methanol exhausted from boiler 34 into reformer 32. The heatedmethanol then enters the reformer chamber 103 at one end of monolithicstructure 100 and passes to the other end where the reformer exhaust isdisposed. In another embodiment, a hole disposed in a reformer 32 wallreceives inlet heated methanol from a line or other supply. The inlethole or port may be disposed on a suitable wall 111 or 113 of reformer32.

Reformer 32 includes a catalyst 102 that facilitates the production ofhydrogen. Catalyst 102 reacts with methanol 17 and produces hydrogen gasand carbon dioxide. In one embodiment, catalyst 102 comprises pelletspacked to form a porous bed or otherwise suitably filled into the volumeof reformer chamber 103. Pellet diameters ranging from about 50 micronsto about 1.5 millimeters are suitable for many applications. Pelletdiameters ranging from about 500 microns to about 1 millimeter aresuitable for use with reformer chamber 103. Pellet sizes may be variedrelative to the cross sectional size of reformer chamber 103, e.g., asreformer chamber 103 increases in size so do catalyst 102 pelletdiameters. Pellet sizes and packing may also be varied to control thepressure drop that occurs through reformer chamber 103. In oneembodiment, pressure drops from about 0.2 to about 2 psi gauge aresuitable between the inlet and outlet of reformer chamber 103. Onesuitable catalyst 102 may include CuZn coated onto alumina pellets whenmethanol is used as a hydrocarbon fuel source 17. Other materialssuitable for catalyst 102 include platinum, palladium, aplatinum/palladium mix, nickel, and other precious metal catalysts forexample. Catalyst 102 pellets are commercially available from a numberof vendors known to those of skill in the art. Catalyst 102 may alsocomprise catalyst materials listed above coated onto a metal sponge ormetal foam. A wash coat of the desired metal catalyst material onto thewalls of reformer chamber 103 may also be used for reformer 32.

Reformer 32 is configured to output hydrogen and includes an outlet port87 that communicates hydrogen formed in reformer 32 outside of fuelprocessor 15. For example, a line 39 may communicate to an anode of fuelcell 20 for electrical energy generation or to a heating port forheating of a catalyst proximate to one or more heat transfer appendages.Port 87 is disposed on a wall of end plate 82 and includes a hole thatpasses through the wall (see FIG. 3B). The outlet hole port may bedisposed on any suitable wall 111 or 113.

Hydrogen production in reformer 32 is slightly endothermic and drawsheat from burner 30. Burner 30 generates heat and is configured toprovide heat to reformer 32. As shown in FIG. 3B, burner 30 comprisestwo burners 30 a and 30 b and their respective burner chambers 105 a and105 b that surround reformer 32. In one embodiment, burner 30 useselectrical resistance and electrical energy to produce heat.

In the embodiment shown, burner 30 employs catalytic combustion toproduce heat. A catalyst 104 disposed in each burner chamber 105 helps aburner fuel passed through the chamber generate heat. Burner 30 includesan inlet that receives methanol 17 from boiler 108 via a channel in oneof end plates 182 or 184. In one embodiment, methanol produces heat inburner 30 and catalyst 104 facilitates the methanol production of heat.In another embodiment, waste hydrogen from fuel cell 20 produces heat inthe presence of catalyst 104. Suitable burner catalysts 104 may includeplatinum or palladium coated onto alumina pellets for example. Othermaterials suitable for catalyst 104 include iron, tin oxide, othernoble-metal catalysts, reducible oxides, and mixtures thereof. Thecatalyst 104 is commercially available from a number of vendors known tothose of skill in the art as small pellets. The pellets that may bepacked into burner chamber 105 to form a porous bed or otherwisesuitably filled into the burner chamber volume. Catalyst 104 pelletsizes may be varied relative to the cross sectional size of burnerchamber 105. Catalyst 104 may also comprise catalyst materials listedabove coated onto a metal sponge or metal foam or wash coated onto thewalls of burner chamber 105. A burner outlet port 89 (FIG. 3A)communicates exhaust formed in burner 30 outside of fuel processor 15.

Some fuel sources generate additional heat in burner 30, or generateheat more efficiently, with elevated temperatures. Fuel processor 15includes a boiler 108 that heats methanol before burner 30 receives thefuel source. In this case, boiler 108 receives the methanol via fuelsource inlet 85. Boiler 108 is disposed in proximity to burner 30 toreceive heat generated in burner 30. The heat transfers via conductionthrough monolithic structure from burner 30 to boiler 108 and viaconvection from boiler 108 walls to the methanol passing therethrough.

Air including oxygen enters fuel processor 15 via air inlet port 91.Burner 30 uses the oxygen for catalytic combustion of methanol. Dewar150 is configured such that air passing through dewar chamber 156receives heat generated in burner 30. Dewar 150 offers thus twofunctions for fuel processor 15: a) it permits active cooling ofcomponents within fuel processor 15 before the heat reaches an outerportion of the fuel processor, and b) it pre-heats the air going toburner 30. Air first passes along the outside of dewar 150 beforepassing through apertures in the dewar and along the inside of dewar150. This heats the air before receipt by air inlet port 93 of burner30. A burner 30 in fuel processor 15 generates heat and typicallyoperates at an elevated temperature. In one embodiment, fuel processor15 comprises a dewar 150 to improve thermal management for fuelprocessor 15. Dewar 150 at least partially thermally isolates componentsinternal to housing 152—such as burner 30—and contains heat within fuelprocessor 15.

Although the present invention will primarily be described with respectto the annular reformer and burner shown in FIGS. 3A and 3B, it isanticipated that fuel cell systems described herein are also applicableto other fuel processor designs. Many architectures employ a planarreformer disposed on top or below to a planar burner. Micro-channeldesigns fabricated in silicon commonly employ such stacked planararchitectures and would benefit from fuel cell systems described herein.Further description of planar fuel processors suitable for use with thepresent invention are included in commonly owned co-pending patentapplication entitled “Planar Micro Fuel Processor” naming Ian Kaye asinventor and filed on the same day as this patent application, which isincorporated by reference for all purposes.

4. Efficient Fuel Cell Systems

Fuel processor components operate at elevated temperatures. Burner 30temperatures from about 200 degrees Celsius to about 800 degrees Celsiusare common. Many fuel cells 20 require elevated temperatures forelectrical energy production. More specifically, the electrochemicalreaction responsible for hydrogen consumption and electrical energygeneration typically requires an elevated temperature. Starttemperatures in the MEA layer 62 and its constituent parts greater than150 degrees Celsius are common.

One embodiment of the present invention heats internal portions of fuelcell 20 using heat generated in fuel processor 15 or gases exhaustedfrom fuel processor 15 that can be used for catalytic combustion in fuelcell 20. FIG. 4A illustrates a heat efficient fuel cell system 400 inaccordance with one embodiment of the present invention. System 400 runsgases exhausted from burner 30 to fuel cell 20 to provide heat to fuelcell 20.

System 400 comprises components of system 10 described with respect toFIG. 1B and also comprises plumbing configured to transport a heatingmedium from fuel processor 15 to fuel cell 20. As the term is usedherein, plumbing may comprise any tubing, piping and/or channeling thatcommunicates a gas or liquid from one location to a second location. Theplumbing may also comprise one or more valves, gates or other devices tofacilitate and control flow. A fan or pump may also be included topressurize a line and move the heating medium. Plumbing between burner30 and fuel cell 20 includes an outlet 402 on fuel processor 15 thatexhausts heated gases from burner 30 to a line 41, which transmits theheated gases to fuel cell 20. A ‘line’ refers to tubing, piping and/orchanneling that is dedicated for fluid or gas communication between twolocations.

In a specific embodiment, line 41 transports the heated gases to fan 37,which moves the heated gases within fuel cell 20 and across the fuelcell stack and heat transfer appendages. Alternatively, the plumbing maybe configured to transport the heating medium from burner 30 to one ormore heat transfer appendages. In this case, line 41 may continuethrough the fuel cell housing and open in the proximity of the heattransfer appendages. A hole in the fuel cell housing then allows line 41to pass therethrough or connect to a port that communicates the gases toplumbing inside the fuel cell for delivery to the fuel cell stack andheat transfer appendage. For catalytic heat generation in fuel cell 20,the plumbing may also transport the heating medium to facilitate gaseousinteraction with the catalyst, such as plumbing delivery to one or morebulkheads.

In one embodiment, the heating medium comprises heated gases exhaustedfrom burner 30. A catalytic burner or electrical resistance burneroperates at elevated temperatures. Cooling air exhausted from anelectric burner or product gases exhausted from a catalytic burner areoften greater than about 100 degrees Celsius when the gases leaves thefuel processor. For many catalytic burners, depending on the fuel sourceemployed, the heating medium is commonly greater than about 200 degreesCelsius when the heating medium leaves the fuel processor. These heatedgases are transported to the fuel cell for convective heat transfer inthe fuel cell, such as passing the heated gases over one or more heattransfer appendages 46 for convective heat transfer from the warmergases into the cooler heat transfer appendages.

In another embodiment, burner 30 is a catalytic burner and the heatingmedium comprises the fuel source. Catalytic combustion in burner 30 isoften incomplete and the burner exhaust gases include unused and gaseousmethanol. Fuel cell 20 then comprises a thermal catalyst thatfacilitates production of heat in the fuel cell in the presence ofmethanol. The fuel source is typically vaporized prior to reaching theburner to facilitate catalytic combustion. In this case, line 41transports the gaseous and unused methanol to the thermal catalyst infuel cell 20. Several suitable thermal catalyst arrangements fortransferring heat into heat transfer appendages 46 were described above(see FIGS. 2A and 2F). Suitable methanol catalysts, such as platinum orpalladium coated onto alumina pellets, were also described above withrespect to catalyst 104 in burner 30.

System 400 also comprises one or more sensors to help regulate thermalmanagement in system 400. A temperature sensor 404 detects temperaturefor a component in fuel processor 15. Sensor 406 may be arranged withinburner 30 for detecting the temperatures within the burner. Othercomponents in fuel processor 15 whose temperature may be monitored bysensor 404 include: reformer 32, boiler 34, boiler 108 and gases at theinlet at outlet ports of each of these components. A temperature sensor406 detects temperature for a component in fuel cell 20. For example,sensor 406 may be arranged in contact with the substrate 89 of one ormore bi-polar plates 44 for detecting the temperature of the plate.Other component in fuel cell 20 whose temperature may be monitored bysensor 406 include: MEA layer 62 and gases in an inlet or outletmanifold. Suitable temperature sensors for use with the presentinvention are widely commercially available from numerous sources knownto those of skill in the art.

FIG. 4B illustrates a heat efficient fuel cell system 420 in accordancewith another embodiment of the present invention. System 420 comprisesplumbing configured to transport a heating medium from reformer 32 tofuel cell 20 to provide heat to fuel cell 20. As shown, line 422transports reformer exhaust from an outlet port of reformer 32 to heattransfer appendage 46. Line 422 may also transport the reformer exhaustto fan 37, which moves the heated gases within fuel cell 20 and acrossthe heat transfer appendages. In another embodiment, reformer 32includes a single output that splits into line 422 for reformer exhaustheating in fuel cell 20 and into line 39 for hydrogen delivery to theanode. A valve may be employed to control flow between the two lines.

In one embodiment, the reformer exhaust is at an elevated temperaturecorresponding to the temperature in reformer 32. Reformer exhausts above100 degrees Celsius are common. Heat in the reformer exhaust thenconvects onto the heat transfer appendage to heat the fuel stack and itsinternal components. In another embodiment, hydrogen production inreformer 32 is often incomplete and the reformer exhaust gases includeunused and gaseous methanol. Fuel cell 20 then comprises a thermalcatalyst that facilitates production of heat in the fuel cell in thepresence of methanol. Boiler 34 vaporizes the methanol prior to reachingreformer 32. In this case, line 422 transports the gaseous and unusedmethanol to the thermal catalyst in fuel cell 20. Suitable methanolcatalysts, such as platinum or palladium coated onto alumina pellets,were also described above with respect to catalyst 104 in burner 30.Alternatively, fuel cell 20 may include a thermal catalyst thatfacilitates production of heat in the fuel cell in the presence ofhydrogen. In this case, the heating medium comprises hydrogen producedin reformer 32. Suitable hydrogen catalysts that help hydrogen produceheat include platinum or palladium, for example. Several suitablethermal catalyst arrangements for transferring heat into heat transferappendages 46 were described above (see FIGS. 2A and 2F).

FIGS. 4A and 4B illustrate two systems 400 and 420 that transport aheating medium from the fuel processor to the fuel cell. The presentinvention may flexibly employ heating from fuel processor 15 to fuelcell 20 for improving efficiency of the fuel cell system. For example, aheating medium may be passed over one or more appendages 46 during startup of fuel cell 20, or during periods of electrical generationinactivity when fuel cell 20 is cooling from elevated temperaturesassociated with operation.

FIG. 5 illustrates a process flow 500 for generating electrical energyin a fuel cell that receives hydrogen from a fuel processor inaccordance with one embodiment of the present invention. The fuelprocessor is configured to process a fuel source to produce the hydrogenand comprises a burner and a reformer.

Process flow 500 begins by providing the fuel source to the fuelprocessor (502). Supply from fuel storage 16 is described above withrespect to FIGS. 1A and 1B. When the fuel processor comprises acatalytic burner, the fuel source is supplied to both the reformer andburner and is used in the burner to generate heat. A catalyst in thereformer receives heat from the burner and reforms the fuel source toproduce hydrogen.

Process flow 500 then transports a heating medium from the fuelprocessor to the fuel cell when a component in the fuel cell has atemperature that is less than a threshold temperature or when electricalenergy output by the fuel cell includes less than an electricalthreshold (504). Electrical energy output by the fuel cell is typicallydc power characterized by a dc voltage and current. The electricalthreshold then refers to a desired electrical output for the fuel cell.For example, if the fuel cell electrical output drops below 0.54 Voltsper cell, then load from the fuel cell may be turned off and the heatingmedium transported from the fuel processor to the fuel cell. Theelectrical threshold may be represented as a desired output according toa polarization curve for the fuel cell, which is stored in softwareavailable to the controller of the fuel cell system. The polarizationcurve represents acceptable electrical energy output for the fuel cell.

For temperature monitoring, the fuel cell component refers to a portionof the fuel cell whose temperature affects fuel cell performance. Thethreshold temperature refers to a desired temperature to begin externalheating of the component. For a functional component of the fuel cell,the threshold temperature may relate to a required temperature for thecomponent to contribute to electrical energy generation. Operatingtemperatures in the MEA 62 and its constituent parts greater than 190degrees Celsius are common. An MEA 62 comprising a Celtec 1000electrolyte from PEMEAS USA AG mentioned above may require operatingtemperatures greater than 100 degrees Celsius. The component mayalternatively comprise a bi-polar plate, a gas diffusion layer, amembrane, or any other component mentioned above with respect to fuelcell 20. The threshold temperature may also vary based on the componentbeing sensed. Detecting temperature of a bi-polar plate on an externalsurface of the fuel cell stack allows the temperature sensor to remainoutside the stack. In this case, the threshold temperature mayaccommodate the difference in temperature between an outside portion ofthe plate where the sensor attaches and an inside portion proximate tothe MEA. Temperature variation in a single plate may range from 2 to 5degrees Celsius for example. In general, the threshold temperature mayvary between about 50 degrees Celsius and about 1000 degrees Celsius forsome fuel cell components.

In one embodiment, the heating medium is transported to the fuel cellduring a start-up period before the fuel cell begins generatingelectrical energy, e.g., in response to a request for electrical energy.Heating a fuel cell in this manner allows fuel cell component operatingtemperatures to be reached sooner and expedites warm-up time needed wheninitially turning on fuel cell 20.

In another embodiment, the heating medium is transported from the fuelprocessor to the fuel cell during a period of non-activity in which thefuel cell does not produce electrical energy and the component cools(502). Since many fuel cells require elevated temperatures for operationand the electrical energy generating process is exothermic, the fuelcell usually does not require external heating during electrical energygeneration. However, when electrical energy generation ceases for anextended time and the component drops below a threshold operatingtemperature, the heating medium may then be transported from the fuelprocessor to regain the operating temperature and resume electricalenergy generation. This permits operating temperatures in a fuel cell tobe maintained when electrical energy is not being generated by the fuelcell.

The heating medium then heats a portion of the fuel cell (506). Theheating medium may comprise heated exhaust (including air, combustionproducts and unused methanol) from a burner or heated exhaust from areformer (including air, reforming reactants and reforming products suchas hydrogen). Heating may also employ catalytic combustion in the fuelcell. During fuel cell system start-up, the reformer may not yet havereached its operating temperature and the exhaust/heating medium maycomprise a high concentration of CO and un-processed fuel (also referredto as ‘dirty hydrogen’) that is unsuitable for use in a fuel cell. Thehydrogen may be catalytically combusted to generate heat in a portion ofthe fuel cell responsible for heat generation. Suitable examples of heattransfer appendage techniques to heat a fuel cell and its internalcomponents with the heating medium are described above.

Process flow 500 detects electrical output of the fuel cell and/ortemperature for the component (510) before transportation of the heatingmedium begins, and afterwards. Logic implemented by a controller thencompares the detected parameter with stored values for either threshold.For detecting current and voltage, the controller logic compares themeasured amount with a stored polarization curve. If the measuredvoltage or current is output by the fuel cell is about equal to orgreater than an electrical threshold, or a shift in the polarizationcurve has occurred, then flow of the heating medium may begin, and insome cases, electrical energy generation may cease. The componenttemperature may similarly be read and compared with stored values.

When the component temperature drops below the threshold temperature orthe electrical output returns to an unacceptable condition, then flow ofthe heating medium may stop, e.g., using a valve between the fuelprocessor and fuel cell. Similarly, if the component temperaturesubsequently rises above the threshold temperature, then flow of theheating medium may again resume. Thus, when needed, process flow 500transports hydrogen from the fuel processor to the fuel cell (508).Electrical energy is generated (512) in the fuel cell when thetemperature of the component is about equal to or greater than thethreshold temperature or when electrical energy output by the fuel cellis about equal to or greater than an electrical threshold.

Efficient systems and methods of the present invention may alsotransport hydrogen in the fuel cell system to burner 30 in fuelprocessor 15. A catalyst in the burner then reacts with the hydrogen toproduce heat in the burner. The hydrogen may come from the anode exhaustof fuel cell 20 and/or from the reformer 32 exhaust.

FIG. 6 illustrates a fuel system 440 that routes unused hydrogen fromfuel cell 20 back to burner 30 in accordance with one embodiment of thepresent invention. Burner 30 includes a thermal catalyst that reactswith the unused hydrogen to produce heat.

Fuel system 440 comprises plumbing that is configured to transporthydrogen to burner 30. Line 51 is configured to transmit unused hydrogenfrom fuel cell 20 to burner 30 of fuel processor 15. For system 440,burner 30 includes two inlets: an inlet 55 configured to receive thehydrogen fuel source 17 and an inlet 53 configured to receive thehydrogen from line 51. Anode gas collection channels, which distributehydrogen provided by fuel processor 15 to each membrane electrodeassembly layer, collect and exhaust the unused hydrogen to a hydrogenexhaust manifold (see FIGS. 2A-2F), which delivers the hydrogen to line51. In one embodiment, gaseous delivery in line 51 back to fuelprocessor 15 relies on pressure at the exhaust of the anode gasdistribution channels, e.g., in the anode exhaust manifold. In anotherembodiment, an anode recycling pump or fan is added to line 51 topressurize line 51 and return unused hydrogen back to fuel processor 15.A fan may also pressurize line 39 to deliver the hydrogen from an outletof fuel processor 15 to an anode inlet of fuel cell 20, which alsopressurizes flow of hydrogen in line 51.

Since hydrogen consumption within fuel cell 20 is often incomplete andthe anode exhaust often includes unused hydrogen, re-routing the anodeexhaust to burner 30 allows fuel cell system 10 to capitalize on unusedhydrogen in fuel cell 20 and increase hydrogen usage and efficiency insystem 10.

Line 442 is configured to transmit hydrogen output by reformer 32 toburner 30 of fuel processor 15. Before a reformer reaches its operatingtemperature upon system start from a cool temperature or rest state,imperfect hydrogen generation at low temperatures may lead to reformeroutput that is unsuitable for use in a fuel cell. In situations wherethe reformer output is unsuitable, fuel system 440 re-routes hydrogenand reformer exhaust to burner 30 via line 442. Burner 30 catalyticallyuses the hydrogen to produce heat. The heat may be provided to thereformer to expedite warm up time for fuel processor 15 and fuel cellsystem 440.

Fuel cell system 440 provides flexibility to use different fuels in acatalytic burner 30. For example, if fuel cell 20 can reliably andefficiently consume over 90% of the hydrogen in the anode stream, thenthere may not be sufficient hydrogen to maintain reformer and boileroperating temperatures in fuel processor 15. Under this circumstance,methanol supply is increased to produce additional heat to maintain thereformer and boiler temperatures.

FIG. 8 illustrates a schematic operation for a fuel cell system 460 inaccordance with another specific embodiment of the present invention.Burner 30 is configured to receive oxygen from an oxygen exhaustincluded in fuel cell 20. Cathode gas collection channels, whichdistribute oxygen and air from the ambient room to each membraneelectrode assembly layer, collect and exhaust any unused oxygen in fuelcell 20. Line 466 receives unused oxygen from an exhaust manifold, whichcollects oxygen from each cathode gas collection channel. Line 466transports the oxygen to an inlet 464 of burner 30. Since oxygenconsumption within fuel cell 20 is often incomplete and the cathodeexhaust includes unused oxygen, re-routing the cathode exhaust to burner30 allows fuel cell system 10 to capitalize on unused oxygen in fuelcell 20 and increase oxygen usage and efficiency in system 10. Fuel cell20 also heats the oxygen before burner 30 receives the oxygen. Oxygen inthe air provided to burner 30 is consumed as part of the combustionprocess. Heat generated in the burner 30 will heat cool incoming air,depending on the temperature of the air. This heat loss to incoming coolair reduces the heating efficiency of burner 30, and typically resultsin a greater consumption of methanol. To increase the heating efficiencyof burner 30, the present invention heats the incoming air in fuel cell20 so less heat generated in the burner passes into the incoming air. Inother words, fuel cell 20 allows pre-heats air before reaching theburner, thus increasing efficiency of system 460.

Fuel cell system 460 also transports unused hydrogen from the anode offuel cell 20 back to the burner of fuel processor 15 for catalyticcombustion and generation of heat. Fuel cell system 460 also employs anelectric heater 462 for heating reformer 32 with electrical energy.

5. Electronics Device Implementation

FIG. 9 shows a schematic illustration of a system 200 for producingelectrical energy in a portable electronics device 202 in accordancewith one embodiment of the present invention. System 200 comprises fuelprocessor 15 and fuel cell 20 included within an electronics device 202and a hydrogen fuel source storage device 16 coupled to electronicsdevice 202 via connector 104 and mating connector 140.

In one embodiment, fuel processor 15 and fuel cell 20 are incorporatedinto electronics device 202 (within its volume and outer housing) as anintegral module, and storage device 16 is a removable device. Fuel cellpowered laptop computers 202 may comprise slightly modified existingproducts, with fuel processor 15 and fuel cell 20 and related systemcomponents fitted generally into the space provided for a battery pack.Mating connector 140 is included in this allocated space for connectionto a removable storage device 16. Storage device 16 mechanicallyinterfaces with electronics device 202. In one embodiment, connectors104 and 140 provide sufficient mechanical force to maintain positionbetween the storage device 16 and electronics device 202. In anotherembodiment, electronics device 202 includes a mechanical slot thatstorage device 16 fits and slides into.

When connector 104 and mating connector 140 interface, fuel cell systemcontroller 214 digitally communicates with memory 206 using link 217 forbi-directional communication therebetween. In another embodiment,controller 214 uses a wireless interrogator to communicate with an RFIDantennae and memory 206 included in storage device 16. Controller 214may read any information stored in memory 206 such as a fuel type storedin the storage device 16, a model number for storage device 16, a volumecapacity for bladder 205 or storage device 16, a number of refillsprovided to storage device 16, the last refill date, the refillingservice provider, and a current volume for the storage device.Controller 214 estimates the remaining power in storage device 16 bycomparing the fuel source 17 level since last use or refill against aconsumption rate for a particular laptop computer. Controller 214 mayalso write transient information to memory 206, such as an updatedvolume for the storage device. The controller 214 communicates with amain controller 210 for computer 202 and computer memory 216 viacommunications bus 212. Computer memory 216 may store instructions forthe control of fuel system 10 such as read and write protocol andinstructions for communication with a digital memory 206.

Power management 219 controls power provision by fuel cell system 10 andelectrochemical battery 222. Thus, power management 219 may informcontroller 214 how much power is needed for laptop computer 22 operationand controller 214 responds by sending signals to fuel cell 20, fuelprocessor 15 and a pump that draws fuel from storage device 16 to alterfuel cell power production accordingly. If fuel cell system 10 runs outof fuel source 17, then power management 219 switches to electricalpower provision from battery 222.

System 200 may also be configured for ‘hot swappable’ capability. Hotswapping of storage device 16 refers to removing storage device 16 froma fuel processor or electronics device 202 it provides hydrogen fuelsource 17 to, without shutting down the receiving device or withoutcompromising hydrogen fuel source provision to the receiving device fora limited time. A hot swappable system implies fuel source provisionwhen connector 104 and mating connector 140 are separated. Furtherdescription of hot swappable fuel cell systems suitable for use with thepresent invention are described in commonly owned co-pending patentapplication entitled “Portable Fuel Cartridge for Fuel Cells” naming IanKaye as inventor and filed on the same day as this patent application,which is incorporated by reference for all purposes.

Main controller 210 is preferably a commercially availablemicroprocessor such as one of the Intel (including Pentium™) or Motorolafamily of chips, a reduced instruction set computer (RISC) chip such asthe PowerPC™ microprocessor available from Motorola, Inc, or any othersuitable processor. Memory 216 may comprise some form of mass storagebut can be eliminated by providing a sufficient amount of RAM to storeuser application programs and data. Memory 216 may also contain thebasic operating system for the computer system. It is generallydesirable to have some type of long term mass storage such as acommercially available hard disk drive, nonvolatile memory such as flashmemory, battery backed RAM, PC-data cards, or the like. Regardless ofcomputer system configuration, it may employ one or more memories ormemory modules configured to store program instructions for controllingfuel cell and thermal systems described herein. Such memory or memoriesmay also be configured to store data structures, control programs, orother specific non-program information described herein.

In addition, although the present invention is primarily described withrespect to fuel cell systems and methods operating on a fuel cellsystem, many of the methods and techniques described constitute systemcontrols and will comprise digital control applied by control logic thatimplements instructions from stored software. The control logic includesany combination of hardware and software needed for control withinsystem 10. For example, the control logic may include instructionsstored in memory 216 that are executed by main controller 210. Thestored instructions may correspond to any methods or elements explainedin the process flows described herein. Input/output logic may beemployed to facilitate communication between main controller 210 andcomponents of fuel system 10. In one embodiment, the control logic isconfigured to regulate heat transfer or temperature in system 10 bycontrolling the routing of liquids and gases between fuel cell 20, fuelprocessor 15 and electronics device 202. In a specific embodiment, thecontrol logic is configured to start fuel system 10. This includescontrol logic configured to start a fuel processor including a reformerand a burner that provides heat to the reformer. In another specificembodiment, the control logic is configured to shut down a fuel cellsystem comprising a fuel cell that received hydrogen from a fuelprocessor including a reformer and a burner that provided heat to thereformer. In another specific embodiment, the control logic isconfigured to regulate the transport of a heating medium from the fuelprocessor to the fuel cell when electrical energy output by the fuelcell includes less than an electrical threshold or when temperature of acomponent in the fuel cell is less than a temperature threshold. In thiscase, memory 216 may include one or more polarization curves that helpdetermine when to transport of the heating medium.

6. Fuel System Start Up

Another aspect of the present invention relates to methods for improvingfuel cell system start up. Fuel cell system components often requireelevated temperatures before electrical energy production occurs.Techniques described herein expedite the time needed for fuel cellsystem start up.

Many fuel processors avoid providing a liquid fuel source to a burner orreformer catalyst. During normal operation, a boiler vaporizes the fuelsource before receipt by the burner or reformer. However, a boiler maynot have sufficient heat during start-up to heat the fuel source. Inthis case, the present invention heats and vaporizes a fuel source usingelectrically generated heat that may be readily turned on during fuelprocessor and system start-up.

FIG. 10A illustrates a system for heating a fuel source before catalyticheat generation within burner 30 in accordance with one embodiment ofthe present invention. As shown, the system includes a fuel processor 15and an electric heater 806. The fuel processor 15 comprises a reformer32, burner 30 and boiler 34, which were described above with respect toFIG. 1A. Reformer 32 comprises a catalyst 804 that facilitates theproduction of hydrogen. Catalyst 804 reacts with methanol 17 andfacilitates the production of hydrogen gas. In one embodiment, catalyst804 comprises pellets packed to form a porous bed or otherwise suitablyfilled into the volume of the reformer chamber.

Burner 30 comprises a catalyst bed 808 that helps a burner fuel passedthrough the burner chamber generate heat. In one embodiment, methanolproduces heat in burner 30 and catalyst 808 facilitates methanol-basedproduction of heat. In another embodiment, waste hydrogen from fuel cell20 produces heat in the presence of catalyst 808. Suitable burnercatalysts 808 may include platinum or palladium coated onto aluminapellets for example.

Electric heater 806 is configured to heat burner 30 or the fuel source17 provided to burner 30. As shown, electrical heater 806 is disposedwithin the burner chamber 810 and intercepts the fuel source 17 beforethe fuel source passes over catalyst bed 808. In this case, a portion ofchamber 810 is reserved for electrical heater 806 and heating of fuelsource 17. A small gap 816 is left between heater 806 and catalyst 808to allow room for the fuel source 17 to heat, vaporize and spread withinthe burner chamber. Gap 816 sizes from about 2 millimeters to about 5millimeters are suitable for many small fuel processors.

Electrical heaters suitable for use in fuel processor 15 may employ aresistive heating element. A rechargeable battery, capacitor or otherelectrical power supply 820 provides electrical energy to heater 806. Inone embodiment, a fuel cell that receives hydrogen from fuel processor15 outputs electrical energy to recharge the capacitor 820. Electricheater 806 may comprise a thin-film platinum, gold, graphite, nickel,chromium, aluminum, alloy or other base metal that may be deposited andused for a resistive heater. A model P/N CSS-01110 cartridge heater asprovided by Omega of Stamford, Conn. is suitable for use as electricalheater 806 in some embodiments.

Electric heater 806 may also comprise a catalyst disposed on an outsidesurface of heater 806 that generates heat in the presence of fuel source17. Platinum, for example, may be coated onto the external surface ofthe heater to interact with fuel source 17 to generate heat in thepresence of the fuel source. The catalytic heat then increases heatgeneration and warming of the incoming fuel source 17.

In another embodiment, electrical heater 806 is embedded in the burnercatalyst bed 808 and heats the catalyst bed 808. In this case, aninsulating cover is used to electrically isolate heater 806 fromcatalyst 808. The insulating cover includes a high temperature,electrically insulating material, such as a ceramic tube. Alternatively,electrical heater 806 may be disposed external to burner 30 and inthermal communication with fuel source supply 27 to heat fuel source 17before it enters burner 30. A heat exchanger may be employed tofacilitate heat transfer between supply 27 line and heater 806.

Burner 30 shows a common inlet 812 that receives both fuel source 17 andair that have been mixed prior to entry into burner chamber 810. Inanother embodiment, burner 30 includes two separate and dedicated inletsfor fuel source 17 and air, respectively. The dedicated fuel sourceinlet may also comprise an atomizing nozzle to facilitate vaporizationof the fuel source.

Thermal communication between burner 30 and reformer 32 also allows heatgenerated by electrical heater 806 to heat fuel source 17 enteringreformer 32. In another embodiment, the present invention employelectrical heat to warm a reformer or reformer catalyst during start-up.FIG. 10C illustrates a system for electrically heating a reformer 32 inaccordance with one embodiment of the present invention.

Reformer comprises an inlet 31 a that receives fuel source 17, catalyst804 and an outlet 31 b that outputs hydrogen gas. In one embodiment,reformer 32 is sized for portable applications and comprises a reformerchamber having a volume greater than about 0.1 cubic centimeters andless than about 50 cubic centimeters. Reformer 32 volumes between about0.5 cubic centimeters and about 2 cubic centimeters are suitable forlaptop computer applications. Further description of annular fuelprocessors suitable for use with the present invention are included incommonly owned co-pending patent application entitled “Annular FuelProcessor and Methods” naming Ian Kaye as inventor and filed on the sameday as this patent application, which is incorporated by reference forall purposes.

Electric heater 806 is configured to heat reformer 32. As shown,electric heater 806 is embedded in the reformer 32 catalyst 804 bed. Aninsulating cover, such as a ceramic tube, electrically isolates heater806 from catalyst 804. In this case, the electric heater 806 appliesheat directly into the reforming catalyst 804 so that the whole fuelprocessor 15 is not heated at startup. This brings the fuel cell online(even at reduced power) faster. In addition, disposing the electricheater 806 in thermal contact with the reformer 32 catalyst minimizesexternal power requirements from a battery or capacitor.

Heater 806 heats reformer 32 or catalyst 804 during fuel processorstart-up. A temperature sensor detects the temperature of the reformercatalyst bed or a wall of reformer 32. When the catalyst 804 reaches adesired temperature for example, heater 806 is turned off. Burner 30comprises an inlet 33 that receives the fuel source 17. A catalyst bed808 in burner 30 heats reformer 32 after electric heater 806 is turnedoff. Electric heater 806 readily thus heats up reformer 32 and allows itto reach operating temperature quickly, with assistance from burner 30if needed and a minimal amount of electrical heat input.

An electric heater may also be employed when the fuel processor isconstructed using MEMS technology. In one MEMs design, a reformercomprises three separate chips: a heater/boiler chip, a reformer/heaterchip and a preferential oxidizer chip. All three chips may have a glasscover and share common manifolds that direct process gasses to thecorrect chip. The heater/boiler chip has a thin film heater deposited inthe flow channels, suitable for use during startup. The heater/reformerand preferential oxidizer chips include MEMS deposited temperaturesensors either on the flow channels, or on the glass cover. Depositionof thin film heaters and sensors is well understood to those of skill inMEMS technology.

FIG. 10B illustrates a process flow 820 for starting up a fuel processorin accordance with one embodiment of the present invention. The fuelprocessor includes a reformer and a burner that provides heat to thereformer. A fuel cell receives hydrogen produced by the fuel processor.

Process flow 820 begins by generating heat using an electrical heaterthat is configured to heat the burner or a fuel source provided to theburner (822). The electrical heater may also be configured to heat thereformer or a fuel source provided to the reformer. The heat mayvaporize the fuel source. The electrical heater generates heat for a setduration or until a particular operating condition is reached. In oneembodiment, the electrical heater generates heat for at least tenseconds before the fuel source is supplied to the burner. Some fuelprocessors may be heated for 30 seconds, up to a minute, or even longer.A threshold start temperature may also be used to determine the heatingduration. A temperature sensitive catalyst, burner or reformer mayrequire that the electrical heater generate heat until the catalyst,burner or reformer reaches a threshold start temperature. Some burnercatalysts include a threshold start temperature above 60 degreesCelsius. Some reformer catalysts include a threshold start temperatureabove 100 degrees Celsius. Alternatively, the electrical heatergenerates heat until the reformer walls reach 150 degrees Celsius orsome other operating temperature. In one embodiment, air and the fuelsource mix before the fuel source reaches the burner and electricalheater. In this case, the electrical heater may be disposed outside theburner to pre-heat the fuel source before entering the burner.

Process flow 820 then supplies the fuel source to the burner (824).Typically, a pump moves the fuel source and turns on via a systemcontroller. The controller may also turn on a fan that provides air tothe burner. A catalyst in the burner then catalytically generates heatin the burner to heat the reformer (826). The fuel source enters theburner before the reformer reaches its operating temperature. If theburner catalyst requires a lower operating temperature than the reformercatalyst, catalytic heat generation in the burner may be used tocontinue heating the reformer—and the electric heater is turned offafter the fuel source is supplied to the burner. If the reformer has notyet reached its operating temperature, the reformer exhaust may comprisea high concentration of CO and un-processed fuel (‘dirty hydrogen’) thatis unsuitable for use in a fuel cell. As described above, the hydrogenmay be routed from a reformer outlet to a burner inlet to react with athermal catalyst in the burner and generate additional heat in theburner to expedite the time needed for the reformer to reach operatingtemperature.

The fuel source is then supplying to the reformer (828). A catalyst inthe reformer then catalytically generates hydrogen (830). Plumbingtransports the hydrogen to a fuel cell that generates electricity usingthe hydrogen. In one embodiment, the electrical heater receives energyfrom a capacitor that is recharged by the fuel cell after the fuel cellsystem gains a steady operating status. The capacitor or rechargeablebattery may also be recharged during system start-up when then fuel cellis at limited capacity, e.g., about 5-15% rated power. At this point,the fuel cell power is enough to operate the electric heater, and thestartup capacitor or rechargeable battery can be turned off orrecharged.

7. Fuel System Shutdown

The present invention also includes methods for shutting down a fuelcell system. FIG. 7 illustrates a process flow 600 for shutting down afuel cell system comprising a fuel cell that received hydrogen from afuel processor in accordance with one embodiment of the presentinvention. The fuel processor includes a reformer and a burner thatprovided heat to the reformer. Process flow 600 is particularly usefulto expunge any liquids in the fuel cell system, including those presentwhen the system is initially shut down and those that accumulate viacondensation as the system cools.

Process flow 600 begins by stopping electrical energy generation in thefuel cell (602). This may occur electrically by varying the charge inthe anode and/or cathode. Hydrogen supply to the fuel cell may also beceased, e.g., using a valve on a line that transports hydrogen to thefuel cell.

Process flow 600 then discontinues a supply of the fuel source to thereformer (604). For system 10 of FIG. 1B, valve 23 disposed on line 29between fuel tank 14 and reformer 32 cuts fuel source provision to thereformer. Cutting power to a pump may also be used to discontinue thefuel supply. Heat is then generated in the burner to heat to thereformer after discontinuing the supply of the fuel source to thereformer (606). In some cases, heat generation in the burner maycontinue for greater than about 30 seconds after discontinuing thesupply of the fuel source to the reformer. Alternatively, heatgeneration in the burner may continue unless the fuel cell load hasdropped below 10% rated power for a few minutes or unless a polarizationcurve for the fuel cell has lowered, e.g., the voltage of the fuel cellhas reduced significantly for a given current.

Heat generation in the burner is then discontinued (608). For anelectric burner, this may be done via an electrical switch or digitalcontrol. For a catalytic burner such as that used in system 10 of FIG.1B, the burner then includes an inlet to receive the fuel source from asupply of the fuel source and the burner catalytically generates heatusing the fuel source. A valve disposed on a line 27 between a fuel tank14 and reformer 32 may cut fuel supply to the reformer. The burner isthen flushed with air (510). Air supply may continue for greater thanabout 60 seconds after discontinuing the supply of the fuel source tothe reformer. Alternatively, air supply may continue until the burnertemperature reaches a threshold cooling temperature, such as 80 degreesCelsius The above steps sufficiently shut down the reformer and ensureno fuel is left in the reformer chamber or burner.

The present invention may also shut down the fuel cell. To do so, air isprovided to a cathode gas distribution system in the fuel cell afterdiscontinuing hydrogen supply to the fuel cell. Powering a fan thatpressurizes air supply to the cathode gas distribution system may dothis. The fuel cell may also be cooled. For system 10 of FIG. 1B, fan 37may be turned on to move cooling air across the heat transfer appendages46 until a desired shut-down temperature is reached. Both fans may rununtil the fuel cell is cooled to a desired temperature and moisture hasbeen removed by the air supply from the cathode gas distribution system.

8. CONCLUSION

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents thatfall within the scope of this invention which have been omitted forbrevity's sake. For example, although the present invention has beendescribed with respect to methods operating on a fuel cell system, manyof the methods and techniques described constitute system controls andwill comprise digital control applied by a processor that implementsinstructions from stored software. While not described in detail, suchdigital control of a mechanical system is well known to one of skill inthe art and the present invention may thus relate to instructions storedin software capable of carrying out methods described herein. It istherefore intended that the scope of the invention should be determinedwith reference to the appended claims.

1. A fuel cell system for producing electrical energy, the fuel cellsystem comprising: a fuel processor that includes a reformer configuredto receive a fuel source, configured to output hydrogen, and includingreformer chamber that contains a catalyst which facilitates theproduction of hydrogen, wherein the reformer chamber has a volumegreater than about 0.1 cubic centimeters and less than about 50 cubiccentimeters; a burner configured to provide heat to the reformer; and afuel cell including a fuel cell stack that is configured to produceelectrical energy using hydrogen output by the fuel processor, the fuelcell stack includes a set of bi-polar plates and a set of membraneelectrode assembly layers, where each bi-polar plate in the stackcomprises i) a substrate, ii) a first channel field including channelsformed as troughs into the substrate for a first surface of the bi-polarplate, ii) a second channel field including channels formed as troughsinto the substrate for a second surface of the bi-polar plate, iii) aheat transfer appendage in material continuity with the substrate and atleast partially arranged external to the fuel cell stack; and plumbingconfigured to transport a heating medium from the fuel processor to theheat transfer appendage.